I understand the spirit of your comment, but now seems like a good time to quote this page that someone posted to HN a couple of months ago:
"Just as there is nothing in the law that permits a person to dump personal property in the public highway, there is nothing that permits the dumping of intellectual property into the public domain — except as happens in due course when any applicable copyrights expire. Until those copyrights expire, there is no mechanism in the law by which an owner of software can simply elect to place it in the public domain."
That's both perhaps true in a hypertechnical sense but largely false in practical substance in the US; there are a number of legal principles (notably promissory estoppel) which make the practical effect of a stated dedication to the public domain by the creator very similar to what it says on the tin, even if the creator technically retains copyright, as it becomes practically, if not technically, impossible to enforce any of the exclusive rights under copyright to restrict downstream actions like copying or creation and distribution of derivative works after such a dedication.
"Just as there is nothing in the law that permits a person to dump personal property in the public highway, there is nothing that permits the dumping of intellectual property into the public domain — except as happens in due course when any applicable copyrights expire. Until those copyrights expire, there is no mechanism in the law by which an owner of software can simply elect to place it in the public domain."
http://www.rosenlaw.com/lj16.htm